Modified colloidal chrysotile and method of preparing same



United States Patent [1.5. Cl. 1623 7 Claims ABSTRACT OF THE DZSCLGSUREChrysotile is subjected to an acidic treatment so as to increase the Si0to MgO ratio from 5% to 30% and the chemically modified chrysotile ismechanically attrited until at least 5% by weight has a particle sizenot exceeding one micron. The microcrystalline colloidal product formsstable, thixotropic dispersions and gels in water and other polarliquids.

This application is a continuation-in-part of copcnding application Ser.No. 436,304, filed Mar. 1, 1965 and now abandoned.

This invention relates to new compositions of matter made by thetreatment of fibrous serpentine asbestos, generally called chrysotile,to produce products of slightly altered chemical composition but of thesame crystal pattern as chrysotile but in microcrystalline colloidalform; to the novel methods by which these new compositions are made, andto new products which can be made from the novel compositions of thisinvention.

A variety of fibrous minerals are known which are generally calledasbestos. Of these, the fibrous form of serpentine-hydrated magnesiumsilicate-known as chrysotile, is perhaps the most abundant, as Well asthe most versatile, principally because of the length and strength ofthe individual fibers. The product is widely used in preparations whereits fibrous nature, combined with its fire resistance, gives it a markedadvantage over other materialsfor example, in the making offire-resistant textiles.

In the preparation of useful articles from the crude chrysotile, theproblem of separating the mineral into usable fibers has involvedconsiderable efiort on the part of asbestos chemists. Mechanicalbreaking of the ore masses results in the production of shortenedfibers, including a considerable percentage of powder, which have beenconsidered of little value.

Chrysotile, as produced by nature, comprises fibers containing bundlesof linear fibrils in an inorganic rock-like matrix. The individualfibrils may have diameters as small as a few hundred angstrom units,while their lengths may be hundreds of microns or much longer. Thefibers are recovered generally from the serpentine rock deposits by avariety of mechanical crushing and screening techniques, which aredesigned to preserve the natural length of the fibers as much aspossible. Substantially all of the effort has been in the direction ofpreserving maximum fiber length in order to get the maximum advantagefrom a physical entanglement of the long fibers or fibrils in makingpaper-like sheets or asbestos yarns or fabrics.

The major efforts in improving dispersions of longfibered asbestos haveinvolved the use of surfactants to permit easier separation of thefibers into individual fibrils of maximum length, usually of the orderof tens of microns-see, for example, the Novak Patent 2,626,- 213,issued Jan. 20, 1953. This approach leads to fibers and fibrilscontaining an organophilic surface coating 3,458,393 Patented July 29,1969 which, of course, may be quite undesirable, especially where theinherent high temperature properties of asbestos are to be utilized tomaximum advantage.

I have discovered that very valuable products can be made fromchrysotile by going in the opposite direction, i.e., by treatingchrysotile to reduce its constituent fibers and fibrils to amicrocrystalline colloidal form possessing a buildup of particles whosemaximum dimension is of the order of under one micron. The resultantproducts have utilities which in certain respects resemble those of theprevious long-fibered asbestos materials and in others resemble thosewhich are obtainable with the far more expensive colloidal forms ofsilica and alumina.

I have discovered that chrysotile can be treated by an appropriatecombination of chemical action and mechanical attrition to produce a newproduct characterized by sub-micron particle size and colloidalproperties, as demonstrated by the ability to form smooth gels in verylow concentrations in water and other highly polar liquids. These smoothgels can be spread out such as by means of a doctor blade and will dryto adherent, cohesive, self-supporting film-like masses without theaddition of further binder. The films resemble paper.

My new particles are useful for the preparation of such films or sheetsand for thickening polar compositions for many industrial uses. Theuntreated asbestos, on the other hand, when given the identicalmechanical disintegration treatment and spread out, gives anon-selfsupporting discontinuous film or coating which has little or noobvious utility.

In accordance with the present invention, chrysolite is treated with anacidic medium so as to increase the weight ratio of Si0 to MgO by fromabout 5% to about 30% preferably 10% to 25%, as compared to that of theparent chrysotile without substantially altering the actual crystalstructure of the chrysotile. Accordingly, a chrysotile having a weightratio of SiO to MgO of 1:1 after treatment with the acidic medium willhave a weight ratio of SiO to MgO of between about 1.05:1 and about1.30:1.

Electron microscopy reveals that the treatment weakens the fibrils byetching their surfaces so that they can readily be reduced to submicronsize by mechanical disintegration, something which is extremelydiificult to do with the untreated extremely resilient fibrils.Furthermore, the treatment also serves to disperse at least some of thefibers into much thinner fibril aggregates. After the treatment, Isubject the material to attrition to produce herein at least about 5% byweight of particles whose maximum dimension is under one micron. Theresultant product, when mixed with water, glycerol, glycols, or similarhighly polar liquids, will produce smooth, highly thixotropic gels atconcentrations of the order of 13%. The particle size distribution ofthe remaining of the treated chrysotile will affect the rheology of thegels. For example, if the major portion of the remainder has a particlesize not greater than 10 microns, the gel will be smoother than a gelformed using a product in which the major portion of the remainder has aparticle size not greater than 30 microns.

The foregoing stated SiO to MgO weight ratio is approximate and is basedupon the generally accepted formula for chrysotile; 3MgO-2SiO '2H O.Chrysotiles from the various world supplies exhibit ratios varying fromabout 0.92:1 to about 1.055 to 1 depending upon the specific source andnatural extraneous impurities. Literature indicates that the SiO mayconstitute from 37% to 44% and the MgO may constitute from 39% to 44%,by weight, of the chrysotile. The present invention is applicable tochrysotile in general.

In the original treatment, the materials which produce the desirablechange in chemical composition consist of essentially any acid or acidsalt. This acid may be weak or strong and the treatment may be at anydesired temperature. However, best results are obtained by treatment atelevated temperatures, preferably the reflux temperature of theparticular treating agent involved, in aqueous suspension at rather lowsolid content. For example, 0.2 N hydrochloric acid can be used to treatchrysotile at about 510% solids for one-half to four hours at reflux.This treatment will produce an optimum increase in the Si to MgO ratioof about 20% for rheology control in polar media. The use of a pressuredigester to permit digestion under pressure permits a reduction in thetime of treatment, as well as in the concentration of acid required toeffect a change to the optimum SiO to MgO ratio.

After treatment, the modified chrysotile is drained and washed withwater, and is then mechanically disintegrated in water or other polarliquid, preferably by a shearing action, as in a Waring Blendor orOsterizer. Other equipment suitable for the mechanical disintegration ofthe acid pretreated asbestos substance is the Cowles Hi-Shear Mixer,such as Model l-VG (Cowles Dissolver Co., Inc., Los Angeles, Calif), orthe Rietz Extructor, also capable of effecting high shear during themechanical disintegration (Rietz Manufacturing Co., Santa Rosa, Calif).Mechanical disintegration or attrition is carried out so as to producemicrocrystalline colloidal segments of the modified asbestos fibrilsthat are submicron in subdivision and until they comprise at least aboutof the mechanically disintegrated product, and preferably comprise fromabout 15 to 20%, or more. The resultant product will form stabledispersions and gels with water and other polar liquids inconcentrations of the order of a few percent.

In the initial treatment, I have obtained satisfactory results withhydrochloric acid, sulfuric acid, nitric acid, an acetylating mixtureconsisting of acetic acid, acetic anhydride, and trace amounts ofsulfuric acid (as used in preparing cellulose acetate), and phosphoricacid. Salts which hydrolyze to produce hydrogen ions are alsosatisfactory and include such salts as the alkali metal acid phosphatesand sulfates, for example, NaH PO NaHSO etc. It is important that theacid be not too concentrated. For example, 0.4 normal sulfuric acid atreflux will remove far too much magnesium oxide in five minutes, causingan excessive change in the SiO to MgO ratio, together with a rapid lossof yield and in gelling properties. On the other hand, an acetylatingmixture of 600 ml. acetic acid plus 110 ml. acetic anhydride plus 3 ml.of concentrated sulfuric acid can be used safely, providing good controlto prevent the reaction from going beyond the desired yield and thedesired SiO to MgO ratio, even after an hour.

Consequently, I prefer to work with dilute acid and have found that 0.2normal strength hydrochloric acid at atmospheric pressure is aboutoptimum from the point of view of getting the reaction completed in ashort time without the danger of too great a loss of product, andwithout severely detracting from the capability of producing stableaqueous dispersions of it when the digestion involves 5% by weight ofchrysotile.

EXAMPLE I Five pounds by weight of chrysotile (Cassiar mine) SiO to MgO,0.99:1 was mixed with 95 pounds by weight of 0.2 normal hydrochloricacid. The product was divided into four equal portions which were heatedat the boil under reflux. A portion of the product was removed at theend of five minutes, fifteen minutes, sixty minutes, and four hours toprovide Samples A, B, C and D, respectively. Each of the portion wasattrited in a Waring Blendor in water at a solids content of 0.5% untilabout 20% by weight of the material was submicron in size.

The amount of submicron material was determined by sedimentation, afterdilution of an aqueous gel to sufficiently low concentration so that theliquid was sufficiently thin to allow heavy particles to separate out.Specifically, I prepared a 1% gel in water and diluted it by a factor often, and adjusted it to pH 3.0 with HCI. A small amount of a dispersingagent may be used to assist in separating the submicron particles moreefficiently and rapidly. This was allowed to stand six hours, and thepercentage of solids in the top fifth of the material measured. Thismaterial, being in Brownian motion, is colloidal; moreover, inspectionunder the microscope indicated it to be substantially of submicron size.The percentage of submicron material in the total sample was calculatedfrom the amount found in the top fifth.

It is not essential that this procedure be followed precisely inmeasuring the content of submicron material. So long as microscopicexamination of the top aliquot reveals the absence of substantially allmaterial above one micron, the method may be used.

Utilizing like conditions, a sample E was prepared by the use of 0.4Normal HCl and heating for five minutes. A sample F was prepared bytreatment with boiling 0.2 Normal H 50 for five minutes and a sample Gwas prepared by the use of 0.4 Normal H The yield and the SiO to MgOweight ratio of each product were determined and are reported in TableI. Portions of the attrited samples were well dispersed at 3% solids inethylene glycol and the apparent viscosity of the dispersion measured ina Brookfield viscometer at 25 C., using a TB 10 spindle at 10 r.p.m.

TABLE I Yield, Percent SiO to MgOz Cps.

as. 4 1. 22 as, 300

Since chrysotile is slightly alkaline, the amount of acid needed willvary somewhat with the percent of chrysotile being treated. Hence, if10% of more solids are being treated with acid, somewhat higherconcentrations are needed.

In the attrition step, the product, which may be used as is on the acidside, or washed substantially free of acid, is subjected to appropriateattrition at high enough solids to form a stiff paste in water. This canbe accomplished on a small scale in a Waring Blendor. In large scaleoperations, a Cowles dissolver or a Bauer refiner (disc mill), or aRietz Extructor are typically useful. Or the acid treatment andappropriate attrition may be performed simultaneously.

When untreated chrysotile is disintegrated into fine particles insimilar machinery, there is little, if any, formation of submicronparticles. The resulting chrysotile will not absorb the liquid firmly,although it will absorb it, and an apparent viscosity can be measureddue largely to the entanglement of fibers into a ropey dispersion. Aftertreatment with an acidic medium to the optimum SiO to MgO ratio andattrition, however, the microcrystalline colloidal rod-like particles ofchrysotile will bind water or other highly polar liquids to form smooth,spreadable, firm gels. It seems clear that the acid treatment not onlyweakens the structure to make it readily reducible in size to submicronstate, but apparently changes the surface character of the particles tomake it more hydrophilic and more compatible with the aqueous medium.However, X-ray studies of the new product show no change in the basiccrystal structure. Moreover, despite the change in the SiO,, to MgOratio, there appears to be no change in infrared spectrum.

One change that does occur is that on differential thermal analysisthere is a marked shift in the valley which normally occurs inunmodified chrysotile at about between 600-700 C., indicating somechanges in the ease with which water is lost in the composition at suchhigh temperatures.

The acid pretreatment in combination with proper attristability of thedispersed product in a solution of a general purpose unsaturatedpolyester, specifically, Laminac 4123, a styrene modified phathalicanhydride-propylene glycol resin. For each of the samples in Table II, astyrene solution of the unsaturated polyester containing tion, inaddition to making it possible to produce micro- 5 approximately 52%solids was prepared. In each instance, crystalline colloidal material ofthe original crystal struca dispersion of 0.25% by weight of the samplewas disture, has still another advantage in that it removes impersed inthe styrene solution by beating in a Waring purities such as iron oxideand other acid-soluble impuri- Blendor at high speed for three minutes.The dispersions ties which are present to a few percent in almost allformed were transferred to test tubes having one inch dichrysotile. Thispurification which takes place as part of ameters and eight inches long,the amount of dispersion the required acid pretreatment, has theadvantage of imbeing sufiicient to fill each tube to the three-quartermark. proving the electrical properties of the material, as well Thetubes were stoppered and stored in the dark for 24 as its whiteness infilm and/or sheet form. hours at which time they were examined. For eachof the As stated hereinabove, the present invention is applisamplesprepared in accordance with the present invencable to chrysotile ingeneral. This may be illustrated by tion, no settling of the dispersedparticles was observed. reference to Table II which sets forth variousproperties In each of the dispersions formed from the chrysotile ofchrysotiles from three world sources and the properties samples whichhad not received the acid treatment prior of these chrysotiles afterbeing subjected to the method to disintegration, settling of theparticles was sufiicient of the present invention. The modifiedchrysotile samples to exhibit a clear layer at the upper portion of thecolumn were prepared by treating the parent chrysotiles at 10% ofliquid. With longer periods of standing, this clear laysolids with 0.4 NCH1 solutions in a high shear mixer, er gradually increasedindepth.specifically a Cowles dissolver, for 30 minutes. The Treatment ofchrysotile in accordance with the present slurry was filtered and thefilter cake washed with the wainvention increases appreciably the oilabsorption propter to remove soluble salts. The Washed filter cake waserties of the chrysotile. Test for the oil absorption was dried in aforced air oven at 100 C. Both the parent made in accordance with ASTMMethod D-281-31 chrysotile samples and the modified chrysotile samples(1966) with the exception that dioctyl phosphate was were fiuffed bybeating dried samples for one minute in a utilized in place of rawlinseed oil and 10 gram samples Waring Blendor at low speed beforesubjecting the samwere used in place of the one gram sample of the ASTMples to the various test procedures. method. In the table, the oilabsorption is reported in Each of the parent chrysotiles and the treatedchrysgrams of dioctyl phthalate to exactly wet 100 grams of otiles wasanalyzed for 510;; and MgO content and the the sample. ratios calculatedfrom these determinations. Similarly, the X-ray diffraction techniqueswere used in obtain X-ray refractive indices were determined both forthe longidefractometer patterns for each of the samples. To illustudinaland transverse axes of the samples. The surface 35 trate differences incrystalographic characteristics, the area of each of the samples wasdetermined by the conareas of two peaks at interplanar spacing, ofvalues at ventional nitrogen adsorption method using the Perkin- 3.65 A.and 7.29 A., were measured. The ratio between Elmer Adsorptometer. thesepeaks as reported in Table II were calculated from Dispersions of eachof the samples in tricresyl phosthe measured areas. phate were preparedand the viscosity of the dispersions From the following table, it isapparent that in each was measured. In each instance, a six gram sample,based of the chrysotiles there was an increase in the surface upon thedry weight, was dispersed in 800 ml. of distilled area of the acidtreated and disintegrated material. The water in a Waring Blendor andagitated at low speed for most notable changes in characteristics arereflected in the ten seconds. The slurry was then filtered in a Bucknersubstantial increase in viscosity when the different matefilter andvacuum disconnected when dripping subsided. rials are dispersed in aliquid such as tricresyl phosphate Five hundred ml. of technicalanhydrous isopropanol was and in the substantial increase in the oilabsorption charthen added to the filter and after seconds the vacuumacteristics. In each instance, the increase is at least about line againapplied until dripping subsided. The filter cake 300%. Probably the mostoutstanding characteristic is was then removed and dried in a forced airoven at 100 the non-settling properties in polyester solutions in the C.for ten minutes. 2.00:0.02 gram of each sample were 50 case of thechrysotiles treated in accordance with the dispersed in a Waring Blendorin 342 ml. of tricresyl present invention.

TABLE II Dispersion in tricresyl Refractive index, phosphate SettlingOil 25 0. Surface in polyesabsorption, X-ray SiOzZMgO area, Viscosity,ter gm. DOP/ area, 3.65 A./ ratio Long. Trans. mfl/gm. poises Typesolution 100 gm. area, 7.29 A.

Quebec chrysotile 0.99 1. 556 1. 548 20 46 (45 C.) Ropey Yes l4 0. 61Acid treated and attrited 1. 17 1. 540 1. 532 180 (47 (3.)... Smooth N o44 0.82 Coalinga chrysotile 0.99 1. 648 1.544 60 16 6 C.) Ropey Yes 120.68 Acid treated and attrited 1.14 1. 540 1. 532 71 132 (46 0.)-.-Smooth- No 5o 0. 74 Shabani chrysotile 1.00 1.548 1. 544 11 153 (510.)..- Ropey Yes. 10 0.58 Acid treated and attrited 1.12 1. 552 1. 54459 446 (40" 0.)--- Smooth No. 40 0.70

phosphate using high speed for two minutes. Each disper- In thecommercial production of products in accordsion was then immediatelytransferred to a jar, the tem- 7 ance with the present invention, thechrysotile may be perature of the dispersion recorded and the viscosity0 treated with the acid solution in a high speed mixer, such measured ina Brookfield viscometer using a RVT Model as a Cowless dissolver, at asolids concentration of about Spindle No. 3 at 2.5 r.p.m. In Table II,the viscosity is re- 10% for a 20 to 30 minute period. Prolonged furtherortedi poises, mechanical disintegration after completion of the reac-The products of this invention exhibit another property 75 tion may becarried out, if desired. The slurry may be not possessed by untreatedchrysotile. This property is the subsequenlty diluted to a 1% to 3%solids concentration and passed through a hydrocycloning unit to removerock and then pumped to a drum filter. The filter cake may be washedwith water to reduce the chlorine content of the cake to about 0.1% orless. The wet cake is removed from the drum filter, pressed to removeexcess water and then transferred to a traveling belt and passed througha drier to reduce the moisture content to about 2% or less. The driedmass may be broken into small fragments or granules for storage andshipment.

Alternatively, after hydrocycloning, the slurry may be pumped to asuitable filter and the filter cake transferred to a tank wheresufficient water is added to form a slurry containing about 0.1% solids.The slurry is then fed to a paper-making machine such as a Fourdrinieror Rotoformer. This high dilution with water inherently reduces thechlorine content. The filter cake in sheet form as produced in thepaper-making type apparatus may be pressed and transferred to a suitablebelt which carries it through drying apparatus. The collected web issubsequently comminuted into small thin chips.

In either case, the crushed filter cake or the Web chips are readilydispersible in water or other liquids by the use of high speed mixingdevices.

As indicated above, the product has utility in the formation of gels atlow solids content, both with water and with hydrophilic polar liquids,such as ethylene and propylene glycols, glycerine, etc. The product alsohas been found to convert silicone oil (such as Dow Corning 710) andtricresyl phosphate into extremely smooth, stable, high viscositygreases, even at concentrations as low as 0.5-3%.

The gels show a marked change in apparent viscosity with. shear rate.When the apparent viscosity is plotted against shear rate on doublelogarithmic paper, there is a straight-line relationship between theapparent viscosity and the shear rate in r.p.m. For example, a 3%dispersion in ethylene glycol of the product obtained according toExample I, using 0.2 normal HCl for fifteen minutes, followed byattrition so that about of the particles are of submicron size, shows adrop in viscosity from something over 300,000 centipoises at 0.5 rpm. toabout 500 centipoise at 100 r.p.m. using a HBT Brookfield viscometerwith TB spindle at C. This sharp reduction in viscosity is a strikingexample of the intense non- Newtonian behavior of these dispersions, andthe useful thixotropic behavior of gels and pastes made from theproduct. Compositions, which are readily thinnable by mechanical actionsuch as stirring or brushing, can readily be made utilizing thefunctional properties of this product. Hence, the product is useful toimpart body to hydrophilic materials without destroying theirworkability-for example, in latex-based paints for false body andleveling control, and in polyester formulations to reduce or eliminateslump. Another use for the material is for bodying of aqueous alkalisolutions. As compared with similar compositions with conventionalthickening agents, compositions made with my new micro-crystallinecolloidal modified chrysotile retain their color, viscosity, and body onstorage, because of its inherent alkali stability.

The innate character of my new product is probably best illustrated bythe fact that gels made therefrom, when cast or spread in thin films,will dry out to smooth, white, opaque, self-supporting sheets which aresufficiently strong so that they can be handled without breaking. Thewhiteness is due partly to the fact that the product has been purifiedwith the removal of iron and similar impurities, and partly due to themore uniform reflection of light by the colloidal size particles.Moreover, the sheets have excellent electrical properties, and thence,are desirable in the production of laminated structures when combinedwith various synthetic resins, and in particular, with hightemperature-resistant resins, wherein the high temperature performanceof asbestos can be utilized in combination with the resins.

These sheets are sufliciently smooth to serve as writing or printingsurfaces, so that with appropriate fire-resistant markings, they canserve for the preparation of fire-resistant records.

Another aspect of my product is that when made into els in liquids suchas glycol, glycerol, or silicone oils, the gels show remarkablestability on being heated. In the case of gels with ethylene glycol, thegels can be heated to over 60 C. with some thinning, but on cooling,they revert to their original viscosities. This is a most unusual anddesirable property in products of this sort, and the combined propertiesof viscosity stability on storage and thermal viscosity stabilityrepresent functional advantages of considerable practical value.

It is obvious that my new products are inexpensive, since they areobtained in high yields from an initially inexpensive material byinexpensive processing steps. Moreover, the less costly and lessdesirable (shorter-fiber) forms of chrysotile, from the point of view oforiginal fiber length, are entirely satisfactory. These forms ofchrysotile can be used to produce products comparable with and superiorto those obtained with submicron colloidal silica spherical particlesand colloidal alumina rod-like particles, which are more expensive toproduce.

The products of this invention are useful for the manufacture offire-resistant sheets, films, fibers, fabrics and the like. Thedispersible modified asbestos may be used alone or incorporated in otherfilament and film-forming substances, such as viscose, cellulose esterand ether solutions, synthetic resin solutions or latexes, polyesters,polyamides, polypropylenes, and the like. Also, the gel may be appliedas a size, leveling agent or binder on paper yarns, or fabrics.

Microcrystalline colloidal silicate from asbestos has also been foundespecially useful for the clarification and densification of sewagesludge when used in dr flour or powder form. Because of its absorptiveproperties for dyes and phenolic compounds, other industrial wastewaters such as dyehouse waste may be effectively treated with this formof modified chrysotile. For these purposes, the product may contain aslow as about 5% of the particles having a maximum particle size of onemicron.

It is an excellent ingredient for column separation and proved effectivewhen used this way for decolorizing a solution of brown sugar.Microcrystalline colloidal silicates in dry powder form can be used tofilter gases such as cigarette smoke because of their unique surfaceaffinity for phenol-based chemicals and other organic compounds. Forexample, they can be an effective filter material for removal ofbenzopyrene in cigarette smoke. Similarly, when added to solutions ordispersions of dyes, they are capable of decolorizing dye solutions.Gels of this product were found to be quite effective in producingstable graphite greases, preventing any separation of the graphiteparticles on standing for long periods of time so that their bodyingaction can be utilized effectively to stabilize suspensions ofparticulate matter such as pigments, etc. The compatibility andstability of these gels in strong acids, as well as acid-salt solutionssuch as ZnCl make them especially useful as long-lasting gelling mediafor leakproof dry cell batteries.

Obviously, departures can be made from specific examples shown in theabove description, without departing from the spirit of the inventionwhich is defined in the claims. More particularly, other acid materialscan be used and other means of attrition, and the product can, ifdesired, be substantially completely reduced to submicron size byattrition, although this is not necessary.

I claim.

1. As an article of manufacture, chemically modified chrysotile at least5% by weight having a particle size not exceeding about one micron andbeing characterized in having a SiO to MgO weight ratio of from about 5%to about 30% greater than the corresponding ratio of the parentchrysotile.

2. An article of manufacture as defined in claim 1 wherein at least 10%by weight of the modified chrysotile has a particle size not exceedingabout one micron and 9 the SiO to MgO weight ratio of the modifiedchrysotile is from 10% to 25% greater than that of the parentchrysotile.

3. An article of manufacture as defined in claim 1 consistingessentially of the chemically modified chrysotile colloidally dispersedin a hydrophilic liquid.

4. An article of manufacture as defined in claim 1 wherein thechemically modified chrysotile is in the form of a self-supportingfibrous sheet.

5. The method of treating chrysotile which comprises 10 subjecting it tothe action of an acidic solution for a time and at a temperatureSufiicient to increase the Si to MgO weight ratio from about to about30% and mechanically attriting the treated chrysotile until at least 5%by Weight has been reduced to a particle size not exceeding about onemicron.

6. The method as defined in claim 5 wherein the chrysotile is treatedwith a solution of a mineral acid.

7. The method as defined in claim 5 wherein the chrysotile is treatedwith a dilute solution of hydrochloric acid at the reflux temperaturefor from about 3-0 minutes to about four hours.

References Cited UNITED STATES PATENTS 130,663 8/1872 Rosenthal 162--31,340,535 5/1920 Garcin 1623 3,031,322 4/1962 Bugosh l06287 X 3,075,8471/1963 Henry l06287 X FOREIGN PATENTS 13,412 5/1928 Australia. 859,0231/ 1961 Great Britain.

HOWARD R. CAINE, Primary Examiner US. Cl. X.R.

PO-l050 Patent No. 3 45 Dated July 29,

Inventor(s) Orlando A Battista It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line Column 4, line "S10 to MgO "dissolver" to Column 5, line"dissolver" to read --to.

subsequently. -hence-.

Column 6, read --Cow1es Dissolver:

47, after "considerable" insert --development--:

(Table I) third column, in the heading should read -Si0 -Dissolver-: 22"CH1" --D1sso1ver.

line 72,

line 76,

to MgO--; change "refiner" should read --HCl--;

line 33 "Cowless dissolver" correct the spelling of Column 6,

line 51, change to -Refiner--.

line 23, change "in" should should Column 7, line 68 change "thence" toread SIGNED AND SEALED MAR 3 11970 Hindu-W11.

WILLIAM E. SGHUIIER, JR. Oonmissloner or flaunt!

